The invention relates to a guide vane ring of a gas turbine engine having guide vanes arranged on two rings which are coaxially and radially at a distance from one another and which are held on assigned housing sections which are exposed to thermally different expansions. One ring is rigidly connected with the guide vanes and the other ring is connected by the compressive force of a tensioning element with free ends of the guide vanes.
A guide vane ring of this type is known from the German Patent Document DE-PS 37 38 439. This is a so-called "semi-integral guide vane ring" in which case either one ring (outer ring) or the other ring (inner ring) is manufactured separately from the vanes and is not a direct fixed component of the guide grid. This type of guide vane ring is used in a gas turbine, preferably in the high-pressure turbine. Because of the high temperature differences occurring there, the guide vane rings expand which results in significant displacements in the radial direction. In addition, axial displacements occur because of the different thermal expansions between the inner and the outer housing which must be mastered for a guide vane ring which is connected with both housings by way of the corresponding rings in order to prevent distortions or even breakage of components.
An integral guide vane ring, i.e., a guide vane ring which is rigidly connected with both rings (that is the outer ring and the inner ring) in this case, would be subjected to considerable thermal tensions. For this reason, the "semi-integral construction" is to be preferred in this case. A problem in the case of a semi-integral guide vane ring are the leakages which occur between the free vane ends and the separate ring.
In the mentioned known case, the separate or other ring and the one ring fixed to the guide vanes are to be arranged to be axially displaceable and are to be pressed against one another by means of a tensioning element. The disadvantage of this arrangement is the fact that, in addition to the mentioned leakages, relatively expensive guiding devices must be provided for the axially movable part, in which case extremely different component temperatures and expansions present problems with respect to the required precise guiding.
It is an object of the present invention to provide a guide vane ring of the mentioned type which, on the one hand, does not impair the axial relative displacements and, on the other hand, drastically minimizes leakages between the free vane ends and the separate sealing ring and can be implemented by means of devices which constructively are as simple as possible.
According to the invention, this object is achieved by a guide vane ring of a turbine of a gas turbine engine having guide vanes arranged on two rings, which are arranged coaxially and radiallly at a distance from one another and which are held on assigned housing sections. The housing sections are exposed to thermally different expansions. One ring is rigidly connected with the guide vanes, and the other ring is connected by the compressive force of a tensioning element with free ends of the guide vanes. The other ring is divided into several piston-ring-type elements which follow one another axially and which are each slotted approximately axially and form a cylindrical sliding surface on which the guide vanes are axially displaceably disposed with their whole free ends. The tensioning element is arranged on the one group of assigned housing sections while forming a radial compressive force which is uniformly distributed on the elements.
The principal advantages of the invention are that the axial relative displacements between the outer and the inner housing or the corresponding sections of these housings and the one ring and the other ring (outer and inner ring) which are respectively connected with it, can be compensated completely in that the free vane tips can slide on the slotted piston-ring-type elements. At least two ring elements, which are arranged axially behind one another, in this case, form a cylindrical sliding surface for the vane tips so that thermally caused relative displacements in the axial direction are possible in an unimpaired manner.
In this context, "Axially slotted" means that a ring element, similar to a piston ring of a reciprocating engine, is interrupted at one point so that certain deformations of the ring element are possible while changing the gap width in the circumferential direction. Preferably the gap of a ring element according to the invention, in the cold state, is approximately 1-5 mm, and particularly 2-3 mm. The size and the shape in the individual case depends on the geometries, materials and temperatures.
The slotted ring elements are arranged such that the axial gaps of the rings are situated in an offset manner with respect to one another in the circumferential direction. Advantageously, only slight leakages will still occur between the gap and the vane tip or tips situated in this area. Gap flows from the delivery side to the intake side through such a gap can be avoided when the "approximately" axial gap of an element is not purely aligned axially but approximately in parallel to the flow direction in the guide vane ring, that is, at an angle with respect to the direction of the axis.
The construction according to the invention may also be used in the case of a radially outer or radially inner ring which is held separate with respect to the vanes.
The respective "other" ring, which, in each case, is not fixed to the vane, may comprise several, thus, for example, two, three or four piston-ring-type elements which are arranged axially behind one another. This has the advantage that the gaps are interrupted in the axial direction, and a possibly non uniform compressive force of the individual ring elements is distributed to several vanes.
The construction according to the invention is particularly suitable for ceramic components; i.e., the semi-integral guide vane ring is made of ceramic materials. In comparison to metallic materials, ceramics have multiple advantages, such as low wear because of the high hardness and high chemical stability; high dimensional stability in a wide temperature range; and arbitrary availability of raw materials. Preferably, the guide vane ring is manufactured of sintered silicon carbide (SSiC) because it maintains it flexural strength up to approximately 1,850K and is distinguished by low thermal expansion, high caloric conductibility, and high sensitivity to thermal shock. However, the guide vane ring or the guide vanes may also be made of metal, in which case protective layers against wear should be provided on the vane tips which rub with the slotted ring elements. The guide vanes may be constructed to be massive (solid) or as hollow vanes.
The slotted ring elements are preferably made of ZrO.sub.2 since this material, on the one hand, is distinguished by a low thermal conduction and, on the other hand, by a low modulus of elasticity, whereby the spring travel becomes longer than when, for example, SiC is used.
In an advantageous further development of the invention, the ring elements are arranged on a supporting ring which is also slotted in the axial direction and on which the tensioning element is supported. As a result, a defined position of the adjacent ring elements can be maintained and leakages can be minimized.
The tensioning element acts in the radial direction in order to, in this manner, press the slotted ring elements against the free vane tips. In this case, the tensioning element is designed as a spring ring which is corrugated in the circumferential direction. Constructively, this development is particularly simple. However, as an alternative, other constructions of the invention are also conceivable, such as single leaf springs or a metallic and thin-walled ring which can be acted upon by pressure on the interior side. In the case of a development as a spring ring, this spring ring is preferably arranged between a housing section of the flow duct and the supporting ring.
Another advantageous development of the invention for a ceramic guide vane ring provides that, between the one, for example, radially outer ring of the guide vane ring and the assigned housing sections, another spring element is provided. In particular, this is constructed as a metallic wire mesh. As a result, the one or radially outer ring with the molded-on guide vanes is centered in the radial direction in a thermally compatible manner, and the forces resulting from the radial displacements between the one radially outer ring and the housing are distributed evenly along the whole circumference, whereby the circumferential torque of the one radially outer ring, which results from the gas forces on the vanes, is elastically supported.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.